Method and means of embossing thermoplastic sheets



L. L. YOUNG A ril 18, 1950 METHOD AND MEANS FOR EMBOSSING THERMOPLASTIC SHEETS Filed July 23, 1946 use MMP OF 3mm Larry %ung ning the material over a metallic roller having an imprint of the desired surface with the thermoplastic coating held against the surface of the roller, subjecting only successive narrow strips taken transversely of the circumference of said roller to a high frequency electro-magnetic field of such magnitude as to raise the said strips of said roller successively to a temperature sufficient to plasticize said thermoplastic coating, whereby said thermoplastic coating receives the imprint of said roller, abstracting heat from said roller at all points of the surface thereof, and maintaining said material in contact with said roller until completion of a heating and subsequent cooling operation has been completed at each element of area of said thermoplastic material.

3. The method of imparting a desired surface to a thermoplastic coating on long flexible sheets of material comprising the steps of: running the material over a metallic roller with the thermoplastic coating against the surface of the roller, inducing eddy currents in successive narrow transverse strips of the circumference of said roller, said eddy current being of such magnitude as to raise the temperature of said strips of said roller successively above that required to plasticize said thermoplastic coating, cooling said entire roller, and maintaining said material in contact with said roller until said heated thermoplastic coating is cooled and solidified.

4. Apparatus for heating a thermoplastic sheet of material comprising, a metallic roller, means for rotating said roller, means at a fixed location for inducing high frequency current in successive thin narrow transverse strips only of the circumference of said metallic roller during the rotation thereof, said metallic roller being elsewhere subject to cooling, said high frequency current being of sufficient magnitude to raise the temperature of said strips while adjacent said fixed location only to a value higher than the temperature of plasticity of said thermoplastic sheet, and means for running the sheet over the metallic roller and against the metallic surface thereof to and beyond said fixed location until said thermoplastic sheet is cooled and solidified. 5. Apparatus for imparting a desired surface to a thermoplastic coating on a long flexible :sheet' of base material comprising, a roller, said 'roller comprising a relatively thin layer of metal secured on a relatively thick base of dielectric material adapted for rapidly abstracting heat from said thin layer ofmetal; means for running said flexible sheet over said roller with said thermoplastic coating held against said metallic surface of said roller; a coil extending along and adjacent to the entire length of said roller externally thereof and subtending a very small arc of the circumference thereof; means for supplying high frequency current to said coil for heating a portion of said layer of. metal located adv jacent to said coil and thereby a corresponding portion of said thermoplastic coating; and means for maintaining said thermoplastic coating in contact with said roller beyond said. very small 4 are for a time suilicient to accomplish cooling of said thermoplastic coating below the temperature of plasticity of said thermoplastic coating before separating said sheet from said roller.

6. Apparatus for imparting heat to a thermoplastic fiexible sheet of material comprising, a rotating roller formed of a dielectric material and having a thin metallic layer on the exterior surface of said rotating roller formed of a dielectric material, means at a fixed location for inducing high frequency current in successive narrow transverse strips of said metallic coating during rotation of said roller, said high frequency current being of such intensity as to raise the temperature of said heated strips in succession above that of the temperature of plasticity of said thermoplastic sheet, means for maintaining said sheet against said roller over a considerable arc thereof, said considerable arc including arc portions at and beyond said fixed locations in the direction of rotation of said roller, and means comprising said dielectric material for rapidly abstracting heat from said thin metallic layer and thereby rapidly cooling said successively heated strips as they passbeyond said fixed location during rotation of said roller, whereby the thermoplastic sheet in contact with said roller is cooled to a temperature sufliciently low to enable solidification of said thermoplastic sheet.

7. The method of subjecting a long traveling sheet of material to rapid heating which comprises running the material around a metallic roller, subjecting successive narrow very thin transverse strips of said roller to a high frequency electro-magnetic field to heat only the said successive strips of the roller, and cooling said strips rapidly after their subjection to said high frequency electro-magnetic field, whereby successive portions of said sheet in contact with the said successively heated and cooled strips are momentarily heated thereby and thereafter cooled thereby.

8. Apparatus for rapidly heating and then cooling a long moving sheet of thermoplastic material which comprises, a metallic member having a relatively large area thereof continually in contact with said sheet, means at a fixed location for inducing high frequency eddy currents in said metallic member and concentrating said eddy currents in a relatively narrow strip only of said relatively large area of said metallic member which is in contact with said moving sheet to heat the said strip only to a high temperature sufiicient to plasticize said material, and means for abstracting heat from all portions of said metallic member continuously, whereby a portion of said sheet is rapidly heated while said portion of said sheet is adjacent said fixed location and is cooled after said portion of said sheet has passed said fixed location;

9. Apparatus for heating a long sheet of thermoplastic material comprising a metallic rotating roller, means "for continuously abstracting heat from all portions of said metallic rotating roller, means for running said sheet over and in continuous contact with said metallic roller, means for inducing high frequency current over a small area onlyof the periphery of said metallic roller, said high frequency current being of sulficientintensity to heat the said small area of said metallic rollerto a high temperature sufiicient to plasticize said thermoplastic material, and means for maintaining said sheet in contact with a relatively large area of said metallic roller including said small heated area of the periphery of said roller and a coated area advanced in the direction of rotation of said rotating roller to cool said thermoplastic material to settin temperature.

LARRY L. YOUNG.

REFERENCES CITED Number 6 UNITED STATES PATENTS Name Date Winnek Oct. 15, 1940 Steinberger May 4, 1943 Wilson May 11, 1943 Crandell July 13, 1943 Ferris Nov. 4, 1947 FOREIGN PATENTS Country Date The following references are of record in the 10 Number file of this patent:

Switzerland Nov. 22, 191"! 

